This present invention relates to ink jet printer apparatus and methods. In particular, the present invention relates to color printing apparatus and methods. More particularly, the present invention relates to continuous ink jet print heads, wherein controlled and variable saturation color printing results from the in-flight mixing of ink containing fluids with a carrier fluid.
Modern color printing relies heavily on ink jet printing techniques. The term xe2x80x9cink jetxe2x80x9d as utilized herein is intended to include all drop-on-demand or continuous ink jet propulsion systems including, but not limited to, thermal ink jet, piezoelectric, and continuous, which are well known in the printing arts. An ink jet printer produces images on a receiver by ejecting ink droplets onto a receiver medium, such as paper, in an image-wise fashion. The advantages of non-impact, low-noise, low-energy use, and low cost operations, in addition to the capability of the printer to print on plain paper, are largely responsible for the wide acceptance of ink jet printers in the marketplace.
Two types of drop-on-demand ink jet printers dominate the market today. Drop-on-demand xe2x80x9cthermalxe2x80x9d ink jet printers, operate by rapidly heating a small volume of ink, which causes the ink to vaporize and expand, thereby ejecting the ink through an orifice or nozzle. The ejected ink thereafter lands on selected areas of a receiving medium. The sequenced operation of an array of such orifices or nozzles moving past a receiver writes a dot pattern of ink on the receiver, forming text or pictorial images. The print head typically includes an ink reservoir and channels that replenish the ink to the region in which vaporization occurs. An example of an arrangement of thermal ink jet heaters, ink channels, and nozzles is disclosed in U.S. Pat. No. 4,882,595 to Truebe et al., entitled xe2x80x9cHydraulically Tuned Channel Architecture.xe2x80x9d
Drop-on-demand piezoelectric printers, on the other hand, operate utilizing a separate piezoelectric transducer for each nozzle, thereby generating a pressure pulse to expel the drops. U.S. Pat. No. 3,946,398 to Kyser et al., entitled xe2x80x9cMethod and Apparatus for Recording with Writing Fluids and Drop Projection Means Thereforxe2x80x9d, describes such a piezoelectric-based printing device. The patent to Kyser et al. discloses a drop-on-demand ink jet printer, wherein a high voltage is applied to a piezoelectric crystal, which causes the crystal to bend. When the crystal bends, pressure is applied and ink reservoir drops are thereafter expelled from the nozzle on demand. In both types of printers, thermal-based and piezoelectric-based, color rendition is accomplished by adding a few (e.g., typically three) color ink reservoirs and associated nozzle and ejection mechanisms so that that different colored dots may be overlaid on appropriate receiving media.
Continuous ink jet systems create a continuous stream of ink drops, generated by periodically perturbing the nozzle with, for example, a piezoelectric transducer. Continuous ink jet printers thus utilize electrostatic charging tunnels placed close to the position where ink droplets are ejected in the form of a stream. Selected droplets are electrically charged via the charging tunnels. The charged droplets are deflected downstream by the presence of deflector plates that have a predetermined electric potential difference between them.
A gutter may be used to intercept the charged droplets, while the uncharged droplets are free to strike the recording medium. Drops not utilized for printing are transferred to the gutter where they can be recycled. Such continuous ink jet printing systems have an advantage over other printing systems because they produce ink drops at a high frequency. However, continuous ink jet printing systems require complicated electrodes and high electromagnetic fields, in addition to the need for a cumbersome and awkward ink recirculation system to recycle unused ink.
The aforementioned printing techniques suffer from several notable drawbacks, including the difficulty to achieve continuous tone (i.e., grayscale) color reproduction. Dithering methods can be utilized to achieve continuous tone color reproduction. However, such dithering methods are utilized at the cost of lower resolution. Another method utilized to provide continuous tone color reproduction involves the deposition of multiple drops from one nozzle onto a single image pixel. However, this method suffers from uncertainty in the exact location of printed pixels because the receiver is typically in motion during printing thereby preventing multiple drops of ink from being released simultaneously.
Such continuous tone color reproduction methods also suffer from the prevalence of image artifacts on final printed images, because less dense image pixels, corresponding to smaller volumes of ink, do not occupy the same area on the receiver as high-density image pixels that correspond to larger volumes of ink. Failure to print pixels of equal area, regardless of image density, is known to produce visual artifacts in printed images.
Another continuous tone color reproduction method involves the use of more than one density of ink to increase the number of levels available for printing. U.S. Pat. No. 5,625,397 to Allred et al., entitled xe2x80x9cDot on Dot Ink Jet Printing Using Inks of Differing Densities,xe2x80x9d describes a method for utilizing two densities of ink, along with multiple droplet deposition, to increase the number of levels available. This method still suffers, to a lesser extent, from the problems mentioned above, as well as creating a new layer of complexity by requiring yet more ink reservoirs and nozzle arrays for each additional density of ink.
Other on-demand printing methods are also known. European Patent Application No. 96104789, describes a method for controlling the intensity in a piezoelectric ink jet drop-on-demand system. In this method, two chambers are connected. Ink in one chamber is injected into a second chamber utilizing a piezoelectric pressure pulse. The mixed fluid is then ejected from the second chamber via another piezoelectric pressure pulse. U.S. Pat. No. 5,606,351 to Hawkins, entitled xe2x80x9cAltering the Intensity of the Color of Ink Jet Dropletsxe2x80x9d describes a method for controlling the intensity in a thermal ink jet drop-on-demand system wherein a secondary chamber containing ink is permitted to mix in a main chamber before the drop is fired.
In all of the above aforementioned printing methods, the number of available color levels is limited due to the number of drops and/or ink densities utilized in printing. In addition, ink is easily wasted. Those systems that do attempt to recycle the ink require complicated electrostatic charging, steering and gutter systems, which are expensive and costly to implement. The print heads utilized in such systems are also based on intricate arrangements of print head arrays, which make cleaning difficult and expensive. Additional nozzles are typically required for multiple ink drops on each pixel.
Based on the foregoing, it can be appreciated that a need exists for a continuous ink jet print head for use in a continuous ink jet printing system that results in improved quality color printed images without the problems that plague printing systems and methods such as those described above.
An object of the present invention is to provide improved image quality in continuous ink jet printing, wherein colored patterns of dots of varying intensities can be placed on a receiver while maintaining pixel size nearly constant on the receiver.
It is another object of the present invention to provide color mixing prior to any ink touching the receiver, utilizing a single nozzle for a three-color printing system.
It is still another object of the present invention to provide a simple monolithic print head.
It is yet another object of the present invention to provide an efficient print head cleaning method and system in which a carrier fluid is utilized to clean the print head without wasting ink.
It a further object present invention to provide a carrier fluid that does not contain ink, wherein the carrier fluid is mixed with ink in-flight to improve print quality on plain paper, without the use of additional nozzles or multiple drops of ink upon each pixel.
With these objects in view, the present invention resides in a continuous ink jet printer, comprising a continuous color ink jet print head composed of a nozzle, pressurized ink sources, and a print head surface having channels disposed therein such that each channel is in communication with the nozzle. The continuous color ink jet print head also includes a microvalve disposed within each of the channels, such that each channel is connected through the microvalve to a pressurized ink source. This configuration permits ink from the pressurized ink source to flow through the channel and thereafter be ejected from the nozzle when the pressurized ink source has attained a particular threshold pressure.
The pressurized ink source functions as an ink reservoir containing fluids in preparation for printing. A continuous jet is formed in the nozzle by the fluids. The microvalve is a thermally activated microvalve that permits colored patterns of dots of varying intensities to be ejected from the nozzle onto a receiver at a constant rate, thereby maintaining a static ink printed pixel size. A range of colored inks can be ejected from the nozzle onto the receiver by selectively controlling the length of time the microvalve is actuated.
A feature of the present invention involves the ability to provide a continuous tone scale for black and white and color images through ink mixing.
It is also a feature of this invention to provide a method for the fabrication of an improved ink jet print head with a minimum number of changes to present fabrication steps.
It is another feature of the invention to establish a method of fluid mixing for two or more fluid components drawn from reservoirs in a controlled manner, so as to achieve a continuous variability in the chemical properties of the mixture on a scale consistent with known print head technologies.
An advantage of the present invention includes an improvement in the color rendition of pictorial images, and the black and white rendition of text and images, particularly in image regions of low color density.
Another advantage of the present invention is an improvement in the speed of printing which may be achieved for a given image quality.
Another advantage of the present invention stems from the mixing of dyes or pigments in the fluid state in a single print head nozzle, so that the pigments and dyes are fully dispersed before application to the receiver.
An additional advantage of the present invention results from the fact that any chemical reactions of the mixed fluids occur in the fluid stream and not on the receiver, thereby affording greater variability in the nature type of receives which may be substituted for one another. The occurrence of chemical reactions in the mixed fluids within the fluid stream also affords greater variability in the nature and type of fluids effecting modulation of color intensity.
These and other objects, features and advantages of the present invention will become apparent to those skilled in the art upon a reading of the following detailed description when taken in conjunction with the drawings wherein there are shown and described illustrative embodiments of the invention.